This invention relates to masters for spirit duplication systems, and more particularly, to non-bleed pre-printed spirit duplicating masters.
With the ever increasing work load on teachers and instructors, it becomes important to use modern technology to relieve the teachers of some of the duties ordinarily undertaken. One tool of frequent use by educators is spirit duplication for producing copies of tests and instructional materials. Conventionally, the instructor types a master from a transfer sheet having coated on the surface thereof a hectographic ink. U.S. Pat. No. 2,748,024 to Klimkowski; U.S. Pat. No. 2,824,812 to Drautz, and U.S. Pat. No. 3,036,924 to Newman, disclose examples of ink compositions which are coated onto transfer sheets for use in a hectographic duplication process. As illustrated in Klimkowski, the image is formed in reverse on a master by transfer from the carbon-type transfer sheet. While Klimkowski discloses use of diazo salt-color former systems, the ink used on such transfer sheets typically contains a wax, a mineral oil and/or fatty acid, a petrolatum, and a dye such as crystal violet.
It has been found that it is also possible to pre-print masters with ink compositions of this type so that the teacher can use such pre-printed masters to make copies for students on a given subject without having to compose the assignment itself. That is, the spirit duplicating ink is reverse printed directly onto the back side of a sheet to form a master, rather than being made by a transfer technique at the time of teacher test preparation. However, in spirit duplicating masters the ink may tend to bleed through the paper to the front surface giving a "halo" effect to the image on the front surface. This is particularly critical in the pre-printed master field since such masters are mass printed months or even years in advance of use and, thus, must be stored for long periods of time. The longer the period of storage, with changes in humidity and temperature taking place during this time, the more chance of a "halo" occurring. Under some circumstances the "halo", if severe enough, renders the sheet aesthetically undesirable or it may even be considered unacceptable because the printing on the front side of the sheet is obscured and rendered unreadable by the "halo".
At present one solution to the "halo" effect is to attempt to obtain as close a registry as possible between the printing on the front surface and the spirit duplicating ink reverse printed on the back side. However, registry is difficult to obtain and even then most of the "halo" problem still exists. In my copending application Ser. No. 490,979, I have disclosed that a more effective solution would be to prevent bleed in the first place.
In addition, known spirit duplicating inks tend to smear and transfer when rubbed and on the application of pressure. Generally a protective tissue layer is used to prevent unintentional transferring and smearing in this manner. If pre-printed masters are used, it is also necessary to use some form of protective device such as individual envelopes, a protective overcoat, or protective tissue sheets.
The necessity of protective tissue sheets is even more evident if a booklet of pre-printed masters is prepared since there is always the danger of transfer of spirit-duplicating ink from the back side of one master to the front of the underlying master. With today's ever increasing cost of paper the use of interspersed tissue layers in such booklets represents a considerable cost factor.
Accordingly, the need exists for pre-printed spirit duplicating masters which do not bleed. While the problem of smearing and bleeding has long been recognized (see, e.g., Drautz, col. 1, lines 14-20), a satisfactory solution has not been yet found. No known spirit-duplicating ink, particularly one capable of being pre-printed on masters, will overcome these problems. Likewise, even though non-bleeding materials, such as cetyl alcohol, are known and have been used in printing inks (see, e.g., Bernstein, U.S. Pat. No. 2,324,671), their only use has been only to reduce the rate of evaporation of the ink composition in a solvent printing process.
Thus, a pre-printed spirit duplicating master which will not bleed or smear is needed in such areas as pre-prepared instructional material.